1. Field of the Invention
The present invention relates to a polishing pad and a polishing method. More particularly, the present invention relates to a polishing pad and a polishing method capable of achieving a better polishing uniformity of a substrate surface.
2. Description of Related Art
As progressing of industries, devices of integrated circuits, microelectromechanical systems, power conversion, communications, storage disks, and displays are becoming more and more advanced and complex. In order to ensure the reliability of the devices, the surface of substrates (e.g., semiconductor wafers, III-V wafers, storage device carriers, ceramic substrates, polymer substrates, and glass substrates) for fabricating these devices must be smooth and even.
Among the planarization processes, a polishing process is often adopted in the industry. Generally speaking, in the polishing process, a pressure is applied on a substrate, so as to press the substrate on a polishing pad, and a relative motion between the substrate and the polishing pad is provided. Through the friction generated by the relative motion, a portion of the substrate surface is removed, such that the surface is planarized gradually.
FIG. 1 is a schematic top view of a conventional polishing pad. The polishing pad 100 includes a polishing layer 110 and a plurality of circumferential grooves 120. The polishing layer 110 is in contact with a surface of a substrate 130. The plurality of circumferential grooves 120 are arranged in concentric circles, and a center of the circumferential grooves 120 coincides with a rotational axis C0 of the polishing pad 100. The circumferential grooves 120 are used to accommodate or remove the polishing residues or byproducts, and enable the substrate 130 to be easily detached away from the polishing pad 100 when the polishing is completed.
During polishing, in addition to the rotation of the polishing pad 100, the substrate 130 on the surface of the polishing pad 100 rotates as well, expecting that all positions of the surface of the substrate 130 are able to contact with the circumferential grooves 120. However, since the circumferential grooves 120 of the conventional polishing pad 100 are concentric circular grooves, and the substrate 130 rotates around its central axis, when a specific point of the substrate 130 moves to a region parallel to tangential direction of the grooves 120, the specific point will be constantly on the groove portion or the non-groove portion. For example, when the specific point is on the groove portion, points near the specific point will be constantly on the non-groove portion, which results in an unfavorable polishing uniformity. In addition, the closer the position is to the central portion of the substrate 130, the more serious the uniformity problem will be. In the entire polishing process, the central portion of the substrate 130 is almost constantly in contact with a specific portion (e.g., the groove portion or the non-groove portion) on the polishing pad 100. Therefore, the polishing rate at the central portion of the substrate 130 will be lower or higher than the polishing rate of other near portions, depending on whether the central portion is constantly positioned on the groove portion or the non-groove portion. The problem that the polishing rate of the substrate 130 is not uniform may eventually suffer the reliability of the devices.
Thus, a polishing pad providing a better polishing uniformity is needed.